I have to say that Risa really transformed. She looked like Koharu when she first joined. But she might've hired a stylist or something - not that it matters. She's got great hair, clothes and at least she tries to speak.
But I think people really need to stop complaining about "that girl is ugly etc". The whole magic of "Morning Musume" is transforming ordinary girls into idols. If they wanted instant idols, the eggs are doing that and whatnot. The whole basis of Morning Musume is how fans get attached to their favourite member and watch them grow, change or struggle.